The invention relates to a shift mechanism for a bicycle gear assembly and in particular a shift mechanism that includes an actuating lever and a release lever that operate independently from each other to shift between the gears.
EP 0 352 733 B1 discloses a shift mechanism for a bicycle gear assembly that is a trigger shift mechanism, in which the tension cable can be wound up against the spring of the bicycle gear and released by a detent mechanism through the actuation of a single lever. This is achieved by an actuating lever rotatably mounted about a central axis to tension the tension cable. One detent device is traversed per shift step. A release lever is actuated to cause the actuating lever to be pulled back by the tension cable into the next detent stage for the next gear ratio. The release lever is an integral part of the actuating lever. The release lever being operated in a plane perpendicular to the plane of operation of the actuating lever. The pivot for the release lever is integrated into the actuating lever and, as the individual gear ratios are selected, corotates about the central axis of the actuating lever. A drawback associated with this configuration is that in the extreme positions of the shift mechanism, between the hill-climbing gears and the speed gears, the actuating lever is located in an area which is ergonomically unfavorable.
French Patent FR 2 701 917 (93 02255) discloses a release lever and an actuating lever that are arranged in two parallel planes of action. This configuration allows an actuating part to be turned by the actuating lever about a common central axis, while the release lever resets the part, gear ratio by gear ratio by means of a toothed rocker bar. The manner in which the rocker bar engages the toothing on the actuating part is similar to a toothed rocker bar in a mechanical clock, which is actuated by a balance.
This invention combines the features of EP 352 733 with the features of FR 2 701 917 inasmuch as a release lever engages a first toothed segment and a release lever acts on a second toothed segment. The release lever and an actuating lever acting in planes that are parallel to one another. The two toothed segments are connected by a detent element designed as a rocker and having detent noses that can alternately engage in one set of toothing of the toothed segments or the other. The detent element is controlled by the release lever. The release lever has a cam contour connected to the detent element by means of an extension. The detent element engages repeatedly and alternately the toothing of the two toothed segments when the release lever is actuated in one direction. The detent element is spring-loaded toward the toothed segment on the actuating lever and thus the detent element is in its rest position when it is engaged with this toothed segment. When the first toothed segment is turned by the actuating lever, the detent element slides over the toothed segment, and the extension of the detent element is released from the cam contour of the release lever without performing an action.
A tension cable, which is wound up by the rotation of the toothed segment by means of the actuating lever, changes gear ratios in the bicycle gear and simultaneously tensions the cable against a spring in the bicycle gear. This tensioning can take place from the first to the last gear ratio. The release lever relaxes the cable and the toothed segments are moved back tooth by tooth, gear ratio by gear ratio. During this process, the release lever""s cam contour, which comprises a rising cam part and a falling cam part, first moves the detent element into a position of engagement and then out of a position of engagement with the toothed segment. If the release lever is released, the extension on the detent element moves backward over the cam contour and a second gear change is performed. The cam contour may be extended to provide a plurality of rising and falling cam parts. This means that a plurality of gears can be shifted in a forward movement of the release lever, an equal number of gear change operations being added during the return of the release lever. Since the actuating lever is connected to the first toothed segment by a pawl, the actuating part is moved by the actuation of the release lever, this movement by the pawl being decoupled from the actuating lever.
It is therefore the object of the invention to create a shift mechanism for actuating a bicycle gear assembly which is designed as a trigger shift mechanism and can actuate a cable to shift one or more gear ratios not just in a direction of rotation corresponding to the winding up of the cable but can also shift via at least one but also via a plurality of gear ratios in a direction of rotation corresponding to the unwinding of the cable through the release of the cable.